b
$As,\,P = \frac{1}{3}\left( {\frac{U}{V}} \right)$
$But\frac{U}{V} = K{T^4}$
$So,P = \frac{1}{3}K{T^4}$
$or\,\frac{{uRT}}{V} = \frac{1}{3}K{T^4}\,\,\,\left[ {As\,PV = u\,RT} \right]$
$\frac{4}{3}\pi {R^3}{T^3} = constant$
$Therfore,T \propto \frac{1}{R}$